This invention relates generally to electric motors, and more particularly, to methods and apparatus for controlling the operation of electric motors.
At least some known fluid handling systems utilize a constant flow rate through a contained space of a system that may include an apparatus for conditioning the temperature of the fluid. Within such systems the rate of fluid flow may be related to the static pressure associated with the system wherein the static pressure may vary due to changes in system flow demands. The apparatus may include an electric motor coupled to a fluid driver such as a fan, a blower, or a pump. The speed and torque of the electric motor may be affected by the static pressure of the system and the rate of fluid flow. The static pressure of the system and the rate of fluid flow may vary according to the changing system demands. Providing systems with motor speed and torque characteristics matched to a fluid mover to provide an approximately constant fluid flow to the system may require laborious and time consuming attempts to match motor speed and torque with the proper fluid mover to at least approximate the desired fluid flow rate for the particular contained space and static pressure of the particular apparatus or the system in which such apparatus was employed.
For example, if the fluid mover is a squirrel cage type blower, a decrease in the static pressure acting on the blower may result in a decrease in the speed of the blower and the electric motor driving it. Conversely, if the static pressure acting on the blower is increased, the speed of the fan and the electric motor may be correspondingly increased. Thus, the speed of squirrel cage type blowers and electric motors varies directly, i.e. in following relation, with a variation of the static pressure.
However, maintaining a substantially constant fluid flow operation with a varying system static pressure may require auxiliary detection and control components that may increase procurement and manufacturing costs beyond those that a customer may be willing to incur.